"The Day We Died" is the third season finale of the Fox science fiction drama television series Fringe.

The finale follows the aftermath of Peter Bishop entering and activating the doomsday device, events which took place in the previous episode.

"The Day We Died" aired on May 6, 2011 in the United States to an estimated 3.0 million viewers, though this number almost doubled once time-shifted views were taken into account.

While its 1.4 ratings share among adults 18 to 49 was an eight percent decrease from the previous episode, it helped Fox tie for first place that night.

The cast were also receptive to the episode, and actor John Noble submitted his performance for consideration at the 63rd Primetime Emmy Awards.

He recognizes the key as from Walter's old home near Reiden Lake and travels there alone, and finds his biological father, Walternate, present.

Walternate admits to being behind the End of Dayers group, as his revenge for Peter activating the doomsday device and destroying the parallel world that was his home.

Walter continues to study the Central Park wormhole and discovers that it links to the past, approximately 250 million years ago.

He comes to realize a temporal paradox (a bootstrap paradox): he will have sent the doomsday device piece by piece into the past, effectively becoming the "First People" mythos, and convinces Peter that they can influence Peter in the past by having him experience the end of days himself and make a different decision when he enters the machine.

While Olivia and Walter and their doppelgangers stare each other down, Peter convinces the two sides to work together to try to repair the damage to save both universes, then suddenly disappears.

The Olivias and Walters cautiously agree that they need to put aside their differences to save both worlds, apparently unaware of Peter's disappearance.

Despite the show not yet being officially renewed for a fourth season,[1] Fringe began casting in mid-March for a "green FBI agent... to come aboard for the finale and possibly recur next year", as reported by E!

[2] TVLine's Michael Ausiello announced later in the month that actress Emily Meade has been cast for the role, describing her character as "a wide-eyed and eager rookie who’s ready to face all of the challenges in front of her", and that she would make her first appearance in the finale.

Pinkner stated in another interview that it "will be as much as anything about setting up next season," and Wyman agreed, writing "It’s like when you read a great novel and you finish a chapter, you’re like, 'Oh my gosh, something happened that’s going to propel me forward!'

In an interview with Entertainment Weekly, actor John Noble noted he liked how the story ultimately ended with having the two Walters "perhaps negotiate a truce and put their minds together" through a "very inventive intervention by Peter, who basically took control of destiny and forced his two fathers to look each other in the eye, as if telling them: Sort it out, gentlemen.

"[20] Joshua Jackson praised the role-reversal of his character with Walter's, "You had Peter wracked with guilt over the circumstances tied to the decision he made [to activate The First People's so-called "doomsday" machine] and clinging to hope that there might be some way out.

"[11] Leading up to the episode's broadcast, Fox released a promotional trailer that recapped relevant scenes and previewed events in the finale.

[22] Fox had previously produced similar trailers for "Entrada", "Marionette", and "Bloodline", three episodes from earlier in the season.

[31] The finale and its lead-in, Kitchen Nightmares, did however help Fox tie for first place in that demographic with ABC and CBS.

[35] Entertainment Weekly's Ken Tucker lauded the finale, commenting in his review's conclusion "Consider about the whole arc of this season and tell me this wasn’t one of the most moving, thrilling, funny, inspiring chunks of television you’ve watched.

"[36] Isler had trouble rating the finale, noting that he had to see how the events are explained in the fourth season before he can make a complete judgment.

Club graded the finale with a B+; he praised the writers "for once again introducing a new world that feels fully formed, with its own rich backstory that they could choose to explore if they have the time and the inclination.

"[37] Murray concluded his review, "It may be that Fringe has bitten off more than it can chew here, and the storytelling is about to get hopelessly convoluted, as it often does once time-travel enters the picture.

And I’m going to trust that no matter how crazy Fringe's fourth season gets, the writers are going to keep bringing everything back to less mind-bending questions".

[43] At the 63rd Primetime Emmy Awards, John Noble submitted "The Day We Died", along with "Entrada" and "The Firefly", for consideration in the Outstanding Supporting Actor in a Drama Series category, but did not receive a nomination.